1. Field of the Invention
The present invention relates to a wide-angle zoom lens applicable for, for example, a silver salt single lens reflex camera or a digital single lens reflex camera, and more particularly, to a zoom lens having an angle of view 2ω of more than 70° at a wide angle end, an F number of about F4 to about F5.6, and a zoom ratio of about 2.4, and an imaging apparatus including the zoom lens.
2. Description of the Related Art
In general, a wide-angle zoom lens for a single reflex lens requires a large back focal length. Therefore, an optical system is configured such that there is strong asymmetry in an optical axis direction. In this structure, lateral chromatic aberration and distortion are increased. In the related art, an aspheric surface is generally used to maintain the performance. As the zoom lens having the above-mentioned structure, Japanese Patent No. 3590807, Japanese Patent No. 3081698, and JP-A-2004-85600 disclose a three-group zoom lens including three lens groups having negative, positive, and positive refractive powers arranged in this order from an object side. In addition, JP-A-2007-156239 discloses a four-group zoom lens including four lens groups having negative, negative, positive, and positive refractive powers arranged in this order from the object side. In the zoom lens disclosed in JP-A-2007-156239, the second lens group is moved in a direction orthogonal to the optical axis in order to correct camera shake.
In general, it is preferable that the performance of a zoom lens be little changed when power varies. In addition, it is preferable that a focus group have a light weight and high operability. In the three-group zoom lens, the entire first lens group is moved for focusing. However, in the three-group zoom lens, since the first lens group has a large outside diameter and a heavy weight, the operability is lowered during focusing. Therefore, for example, as in the zoom lens disclosed in Japanese Patent No. 3590807, an inner focus system has been proposed in which a positive second lens group is moved toward an image surface during focusing on a short-distance object point. In this case, it is considered to increase the number of lens groups divided, in order to improve a zoom performance and a focus performance. JP-A-2007-156239 discloses a zoom lens that includes four lens groups in order to correct camera shake, not in order to improve the zoom performance and the focus performance.